Automotive alternators that use Lundell rotors have been used in automobiles for decades. Loads from electrical equipment that is mounted due to environmental issues have been increasing rapidly in recent years, and further increases in generated power are being sought from Lundell rotors.
Increasing field magnetomotive force of the rotor is most effective for increasing output of Lundell dynamoelectric machines. However, if the amount of magnetic flux that passes through the rotor is increased by increasing the field magnetomotive force, sizes of respective portions of the rotor are consequently required to be designed such that appropriate magnetic flux density is achieved so as to avoid magnetic saturation of rotor magnetic path portions. From a design perspective, it is necessary to ensure that yoke portions are not magnetically saturated from root portions of claw-shaped magnetic pole portions.
In magnetic path design of a Lundell rotor, methods have been proposed in which design is performed such that magnetic path cross-sectional area of a yoke portion is sufficiently large relative to root magnetic path cross-sectional area of claw-shaped magnetic pole portions as a design that alleviates magnetic saturation of the rotor (see Patent Literature 1, for example).